Random Telegraph Signals and 1/f Noise in ZnO Nanowire Field Effect Transistors

Single-crystal ZnO nanowires have been fabricated as field effect transistors (FETs). The low frequency noise in the drain current of n-type ZnO FETs has been investigated through random telegraph signals (RTSs) at 4.2 K and 1/f noise at room temperature. At room temperature, the noise power spectra have a classic 1/f dependence with a Hooge parameter that is similar to 5 x 10(-3). ZnO FETs measured in a dry O-2 environment displayed elevated noise levels that can be attributed to increased fluctuations associated with O-2(-) on the 2 nanowire surfaces. At 4.2. K, the device's noise spectra change from 1/f to Lorentzian type, and the current traces as a function of time show random telegraph signals (RTSs). The channel current RTSs are attributed to correlated carrier number and mobility fluctuation due to the trapping and emission of carriers by discrete border traps. At certain bias conditions, the current in the channel shows three-level switching events with amplitudes as high as 40 %, from which two individual defects with energies close to the Fermi level in the ZnO channel can be distinguished.